我们知道了沼气是非常好的能源物质，可以用来烧锅炉、发电、提纯生物天然气或者重整制氢。但是沼气中含有很多杂质，需要先经过一定程度的净化才能进行利用。净化程度一般需要根据沼气用途确定，通常需要去除的主要是水、硫化氢和粉尘颗粒。另外如果沼气用于提纯天然气或者重整制氢，氧气、氮气及挥发性有机物等杂质也是需要去除的。? ?注：本表部分信息引自邓良伟等《沼气工程》；

　　We know that biogas is a very good energy material that can be used to burn boilers, generate electricity, purify natural gas, or produce hydrogen through reforming. However, biogas contains many impurities and requires a certain degree of purification before it can be utilized. The degree of purification generally needs to be determined based on the use of biogas, and the main substances that need to be removed are water, hydrogen sulfide, and dust particles. In addition, if biogas is used for purifying natural gas or reforming hydrogen, impurities such as oxygen, nitrogen, and volatile organic compounds also need to be removed.? Note: Some information in this table is quoted from Deng Liangwei et al.'s "Biogas Engineering";

　　沼气净化环节，虽然在整个沼气工程中占比不大，但又是一个不可忽略的环节，也需要专业的厂家去做。这部分项目额度不高，工作琐碎，愿意去做精做好的厂家其实并不多。但是沼气工程就是这样，由一个又一个的环节串联而成，只有每个环节都做好了，整个项目才可能好。

　　The biogas purification process, although accounting for a small proportion in the entire biogas project, is still an essential step that cannot be ignored and requires professional manufacturers to do it. This part of the project does not have a high budget, and the work is tedious. There are actually not many manufacturers willing to do it well. But biogas engineering is like this, consisting of one link after another, and only when each link is done well, can the entire project be successful.

　　本篇，我主要总结了沼气净化环节中最重要的三块内容：硫化氢的去除、水蒸气的去除和粉尘颗粒的去除。

　　In this article, I mainly summarized the three most important aspects of biogas purification: removal of hydrogen sulfide, removal of water vapor, and removal of dust particles.

　　1沼气中硫化氢去除

　　1. Removal of hydrogen sulfide from biogas

　　沼气中最讨厌的一个杂质就是硫化氢，尤其蛋白质含量比较高的物料产出的沼气，硫化氢含量也会比较高。硫化氢具有较强的腐蚀性和毒性，应最先被去除。硫化氢去除一般分为：生物脱硫、化学脱硫、物理脱硫。化学脱硫又分为湿法脱硫和干法脱硫。物理脱硫法一般是采用活性炭吸附，这种方法成本较高，一般较少采用。目前采用较多的是生物脱硫、湿法脱硫和干法脱硫。

　　The most disliked impurity in biogas is hydrogen sulfide, especially in biogas produced from materials with high protein content, where the hydrogen sulfide content is also relatively high. Hydrogen sulfide has strong corrosiveness and toxicity, and should be removed first. Hydrogen sulfide removal is generally divided into biological desulfurization, chemical desulfurization, and physical desulfurization. Chemical desulfurization is divided into wet desulfurization and dry desulfurization. The physical desulfurization method generally uses activated carbon adsorption, which is costly and rarely used. At present, biological desulfurization, wet desulfurization, and dry desulfurization are commonly used.

　　（1）生物脱硫生物脱硫是利用特定微生物将沼气中的H2S转化为单质硫或硫酸盐的脱硫方式。基本原理是：H2S被微生物吸收转移至微生物体内，作为营养物质被特定的微生物分解、转化、利用，微生物得以生长繁殖。常见的生物脱硫有原位生物脱硫（即厌氧罐内生物脱硫），滴滤工艺（也称酸式/一体式生物脱硫），洗涤再生工艺（也称碱式生物脱硫/分离式生物脱硫）。

　　(1) Biological desulfurization is a desulfurization method that uses specific microorganisms to convert H2S in biogas into elemental sulfur or sulfate. The basic principle is that H2S is absorbed and transferred by microorganisms into their bodies, and as a nutrient, it is decomposed, transformed, and utilized by specific microorganisms, allowing them to grow and reproduce. Common biological desulfurization methods include in-situ biological desulfurization (i.e. anaerobic tank biological desulfurization), drip filtration process (also known as acid/integrated biological desulfurization), and washing regeneration process (also known as alkaline biological desulfurization/separated biological desulfurization).

　　（2）湿法脱硫湿法脱硫是利用特定的溶剂与气体接触而吸收其中的H2S，溶剂失效后通过再生重新使用。湿法脱硫按溶液的吸收与再生性质又可分为氧化法、吸收法。氧化法是借助溶液中载氧体的催化作用，将吸收的硫化氢转化为硫磺，使溶液获得再生。氧化法主要有氨水法、砷碱法、蒽醌二磺酸钠法等。吸收法以弱碱性溶液为吸收剂，与硫化氢进行化学反应形成化合物，当富液温度升高、压力降低时，该化合物就分解，放出硫化氢。这类方法有烷基醇胺法、碱性溶液法等。其中最常用的是碳酸钠吸收法。由于碳酸钠溶液在吸收酸性气体时，pH 不会很快发生变化，保证了系统的操作稳定性。此外，碳酸钠溶液吸收硫化氢比吸收二氧化碳快，可以部分地选择吸收硫化氢。该法通常用于脱除气体中大量二氧化碳，也可以用来脱除含二氧化碳和硫化氢的天然气及沼气中的酸性气体。

　　(2) Wet flue gas desulfurization is the process of using a specific solvent to absorb H2S from a gas, which is then regenerated and reused after the solvent has failed. Wet desulfurization can be divided into oxidation method and absorption method according to the absorption and regeneration properties of the solution. The oxidation method utilizes the catalytic effect of oxygen carriers in the solution to convert absorbed hydrogen sulfide into sulfur, thereby regenerating the solution. The oxidation methods mainly include ammonia method, arsenic alkali method, sodium anthraquinone disulfonate method, etc. The absorption method uses a weakly alkaline solution as an absorbent and reacts chemically with hydrogen sulfide to form a compound. When the temperature of the rich solution increases and the pressure decreases, the compound decomposes and releases hydrogen sulfide. This type of method includes alkyl alcohol amine method, alkaline solution method, etc. The most commonly used method is the sodium carbonate absorption method. Due to the fact that the pH of sodium carbonate solution does not change quickly when absorbing acidic gases, the operational stability of the system is ensured. In addition, sodium carbonate solution absorbs hydrogen sulfide faster than carbon dioxide, and can partially selectively absorb hydrogen sulfide. This method is usually used to remove large amounts of carbon dioxide from gases, and can also be used to remove acidic gases from natural gas and biogas containing carbon dioxide and hydrogen sulfide.

　　（3）干法脱硫：干法脱硫按原理可分为化学吸附法和化学吸收法。化学吸附法即采用脱硫剂吸附气体中的硫化物从而达到脱硫的目的，活性炭和分子筛吸附即属此类。化学吸收法即采用脱硫剂与气体中的硫化氢反应将硫化物脱除的过程，其脱硫剂有氧化铁、氧化锌、氧化锰等。近代工业上也常用干法脱硫作为脱除有机硫和精细脱硫的手段。其中氧化铁资源丰富，价廉易得，是目前使用最多的沼气干法脱硫方法。三种脱硫工艺总结如下图：

　　(3) Dry desulfurization: Dry desulfurization can be divided into chemical adsorption method and chemical absorption method according to the principle. Chemical adsorption method uses desulfurizers to adsorb sulfides in gases to achieve desulfurization, and activated carbon and molecular sieve adsorption belong to this category. Chemical absorption method is the process of removing sulfides by reacting desulfurizers with hydrogen sulfide in the gas. The desulfurizers include iron oxide, zinc oxide, manganese oxide, etc. Dry desulfurization is also commonly used in modern industry as a means of removing organic sulfur and fine desulfurization. Among them, iron oxide resources are abundant, inexpensive and easy to obtain, and it is currently the most commonly used dry desulfurization method for biogas. The summary of three desulfurization processes is shown in the following figure:

　　2沼气中水蒸气去除

　　2. Removal of water vapor from biogas

　　前面说到，沼气中还含有水蒸气，一般发酵罐中沼气相对湿度达到 100%，这也意味着沼气中水蒸气是饱和状态。水蒸气与H2S、NH3、CO2反应，会引起后续设备严重磨损和损坏，因此沼气必须进行干燥处理，去除过多的水分。一般可使用的干燥沼气的方法有:冷凝脱水、溶剂吸收脱水、干燥剂吸附脱水。三种脱水工艺总结如下。

　　As mentioned earlier, biogas also contains water vapor. Generally, the relative humidity of biogas in a fermentation tank reaches 100%, which also means that the water vapor in biogas is saturated. The reaction between water vapor and H2S, NH3, CO2 can cause severe wear and damage to subsequent equipment, so biogas must be dried to remove excessive moisture. The commonly used methods for drying biogas include condensation dehydration, solvent absorption dehydration, and desiccant adsorption dehydration. The three dehydration processes are summarized as follows.

　　（1）冷凝脱水：

　　(1) Condensation dehydration:

　　①原理：冷凝法的原理是将沼气冷却到水蒸气露点温度以下，再进行水的分离。

　　① Principle: The principle of condensation method is to cool biogas to below the dew point temperature of water vapor, and then separate the water.

　　②常用形式：气水分离器、沼气凝水器、冷干机/冷水机组+换热器

　　② Common forms: gas water separator, biogas condenser, refrigerated dryer/chiller+heat exchanger

　　③适用性：冷却脱水精度取决于冷却温度和分离手段，冷却温度越低，脱水效果越好，但能耗也越高，因此，适合用在脱水精度要求不高的场合，特别适用于“大气量，大分离”的工况，在脱水精度较高的工况可作为初步脱水

　　③ Applicability: The accuracy of cooling and dehydration depends on the cooling temperature and separation method. The lower the cooling temperature, the better the dehydration effect, but the higher the energy consumption. Therefore, it is suitable for use in situations where dehydration accuracy is not high, especially for "atmospheric volume, large separation" conditions. In conditions with high dehydration accuracy, it can be used as a preliminary dehydration

　　④优点：流程简单、操作简便、处理能力大、运行稳定、投资及运行费用低。除水蒸气外，其他杂质(如水溶气体、气落胶)也会在冷凝中被去除。

　　④ Advantages: Simple process, easy operation, large processing capacity, stable operation, low investment and operating costs. In addition to water vapor, other impurities such as water-soluble gases and gas droplets will also be removed during condensation.

　　⑤缺点：由于降温程度有限，该方法无法做到100%脱水(即脱水精度低)，在脱水精度要求较高的工况只能作为气体深度脱水干燥的初步处理手段。

　　⑤ Disadvantages: Due to limited cooling, this method cannot achieve 100% dehydration (i.e. low dehydration accuracy), and can only be used as a preliminary treatment method for gas deep dehydration and drying in working conditions with high dehydration accuracy requirements.

　　（2）溶剂吸收脱水：

　　(2) Solvent absorption dehydration:

　　①原理：溶剂吸收法是利用吸水性能高的液体作为干燥剂，与通过吸收塔的气体逆流接触，从而进行气液传质以脱除气体中的水分的方法。常用的吸收剂有乙二醇、二甘醇、三甘醇、可吸湿盐类等。

　　① Principle: Solvent absorption method is a method of removing water from gas by using a liquid with high water absorption performance as a desiccant and contacting it in reverse flow with gas passing through an absorption tower, thereby performing gas-liquid mass transfer. Common absorbents include ethylene glycol, diethylene glycol, triethylene glycol, and hygroscopic salts.

　　②适用性：适用于“大气量、小吸收”的工况，在大气量脱水干爆的工业生产中可以按先冷凝脱水，再溶剂脱水的工艺进行搭配使用

　　② Applicability: Suitable for working conditions of "atmospheric volume, small absorption", it can be used in combination with the process of first condensing dehydration and then solvent dehydration in industrial production of large volume dehydration and dry explosion

　　③优点：流程简单、处理能力大、气体压降较小、运行稳定、运行费用较低;溶剂吸收的脱水精度较冷凝法的高。

　　③ Advantages: simple process, large processing capacity, low gas pressure drop, stable operation, and low operating costs; The dehydration accuracy of solvent absorption is higher than that of condensation method.

　　④缺点：湿气的流量、温度、压力和溶剂的浓度、温度、循环量以及干燥塔的设备结构都会对溶剂吸收法脱水效果造成一定的影响，运行成本相对冷凝法高。

　　④ Disadvantages: The flow rate, temperature, pressure of moisture, concentration, temperature, circulation rate of solvent, and equipment structure of the drying tower will all have a certain impact on the dehydration effect of solvent absorption method, and the operating cost is relatively high compared to condensation method.

　　（3）干燥剂吸附脱水

　　(3) Desiccant adsorption dehydration

　　①原理：干燥剂吸附脱水是利用多孔性的固体材料吸附沼气中的水蒸气，如二氧化硅、氧化钼、氧化镁、活性炭和沸石等。

　　① Principle: Desiccant adsorption dehydration is the use of porous solid materials to adsorb water vapor from biogas, such as silica, molybdenum oxide, magnesium oxide, activated carbon, and zeolite.

　　②适用性：适用于中小气量脱水，或作为另外两种脱水方式的补充

　　② Applicability: Suitable for dehydration of small and medium gas volumes, or as a supplement to the other two dehydration methods

　　③优点：脱水精度高，对气体温度、压力、流量变化不敏感，操作弹性大，占地面积小，操作易于程序化控制

　　③ Advantages: High dehydration accuracy, insensitivity to changes in gas temperature, pressure, and flow rate, high operational flexibility, small footprint, easy to program control operation

　　④缺点：工艺复杂、气体压降较大、吸附剂需定期更换、运行能耗较高;对于处理气量大的气体，设备投资较大，运行费用也比较高。

　　④ Disadvantages: complex process, high gas pressure drop, adsorbent needs to be replaced regularly, high operating energy consumption; For gases with large processing volumes, equipment investment is relatively high and operating costs are also relatively high.

　　3沼气中粉尘去除

　　3. Dust removal from biogas

　　水洗除尘：

　　Water washing and dust removal:

　　①原理：通过洗涤方式，将沼气中粉尘去除

　　① Principle: Remove dust from biogas through washing method

　　②适用范围：沼气脱硫前，去除大颗粒杂质

　　② Scope of application: Removing large particle impurities before biogas desulfurization

　　③优点：不需要更换滤芯，运行成本低，可自动化控制

　　③ Advantages: No need to replace filter element, low operating cost, and can be automatically controlled

　　④缺点：去除精度低;无法用于干燥后除尘

　　④ Disadvantages: Low removal accuracy; Cannot be used for dust removal after drying

　　过滤除尘：

　　Filtering and dust removal:

　　①原理沼气通过过滤器，将沼气中的粉尘去除

　　① Principle: Biogas is filtered to remove dust from the biogas

　　②适用范围：脱硫后，沼气利用前，以及对进气有较高要求的情况

　　② Scope of application: After desulfurization, before biogas utilization, and situations with high requirements for intake air

　　③优点：设备简单，去除效率高，去除精度高，可用于各阶段除尘

　　③ Advantages: Simple equipment, high removal efficiency, high removal accuracy, can be used for dust removal in various stages

　　④缺点：过滤器滤芯需要经常更换，成本稍高

　　④ Disadvantage: The filter cartridge needs to be replaced frequently, resulting in slightly higher costs

　　前文我们说到，一部分固体颗粒会被水蒸气或者沼气带出，我们称之为粉尘，这些粉尘如不去除，会在压缩机、气体储罐、发电机中沉积，引起管道堵塞、增大磨损、降低设备寿命等。沼气中的粉尘去主要有两种方式：洗涤除尘和过滤除尘。

　　As mentioned earlier, some solid particles are carried out by water vapor or biogas, which we call dust. If these dust particles are not removed, they will deposit in compressors, gas storage tanks, and generators, causing pipeline blockage, increased wear, and reduced equipment life. There are two main ways to remove dust from biogas: washing and filtering.

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